1. Field of the Invention
The present invention relates to a phosphor (fluorescent material) comprising, as a host crystal, an AlN crystal (aluminum nitride crystal), an AlN polytype crystal, or an AlN solid solution crystal; a manufacturing method thereof; and an application thereof. More specifically, the application relates to an emission apparatus of a lighting device and an image display device utilizing features of the phosphor, that is, property of emitting blue light having a peak in a wavelength range of 430 nm or longer and 480 nm and shorter. In particular, it relates to the image display device with excitation by an electron beam whose acceleration voltage is at least 10 V.
2. Background Art
The phosphor is utilized in a fluorescent display tube (VFD: vacuum-fluorescent display), a field emission display (FED: Field Emission Display) or SED (Surface-Conduction Electron-Emitter Display), a plasma display panel (PDP: Plasma Display Panel), a cathode-ray tube (CRT: Cathode-Ray Tube), a white light-emitting diode (LED: Light-Emitting Diode), and so on. In any of these applications, it is necessary to provide the phosphor with energy to excite the phosphor in order to make the phosphor emit the fluorescence and the phosphor is excited by an excitation source with high energy such as a vacuum ultraviolet ray, an ultraviolet ray, an electron beam, blue light, or the like so as to emit visible light rays. However, as a result of the phosphor being exposed to such excitation source, the luminance of the phosphor tends to decrease and a phosphor having little degradation in the brightness is desired. Therefore, it has been proposed to utilize a sialon phosphor, an oxynitride phosphor, and a nitride phosphor as a phosphor having little degradation in brightness instead for the conventional phosphor such as a silicate phosphor, a phosphate phosphor, an aluminate phosphor, and a sulfide phosphor.
An example of the sialon phosphors is manufactured by a manufacturing process as generally described below. First, silicon nitride (Si3N4), aluminum nitride (AlN), and europium oxide (Eu2O3) are mixed in predetermined molar ratios and the resultant mixture is fired by a hot press method in one atmospheric pressure (0.1 MPa) of nitrogen atmosphere at 1700° C. for one hour (for example, refer to Patent Document 1). It was reported that α-sialon activated with an Eu ion (Eu2+) manufactured by the above process had became a phosphor emitting yellow light in a wavelength range of 550 nm to 600 nm if excited by blue light having a wavelength range of 450 to 500 nm. A phosphor in which a rare-earth element is added to β-type sialon is also known (refer to Patent Document 2) and it is shown that phosphors activated by Tb, Yb, and Ag become phosphors emitting green light of 525 nm to 545 nm. It is also known that β-type sialon activated by Eu2+ becomes a phosphor of green color (refer to Patent Document 3).
As an example of the oxynitride phosphor, a blue phosphor activated by Ce and having a host crystal of JEM phase (LaAl(Si6-zAlz)N10-zOz) (refer to Patent Document 4) and a blue phosphor activated by Ce and having a host crystal of La3Si8N11O4 (refer to Patent Document 5) are known.
As an example of the nitride phosphor, a red phosphor activated by Eu and having a host crystal of CaAlSiN3 is known (refer to Patent Document 6). Moreover, it was reported in Nonpatent Document 1 that an orange or red phosphor having an emission peak from the Eu ion (Eu3+) in the range of 580 nm to 640 nm had been obtained, as a phosphor having AlN as a host, by synthesizing an amorphous ceramic thin film of phosphor activated by a trivalent Eu ion (Eu3+) (i.e., AlN: Eu3+) at the room temperature with a magnetron sputtering method. In Nonpatent Document 2, it was reported that a phosphor of amorphous AlN thin film activated by Tb3+ had emitted green light having a peak at 543 nm upon excitation by an electron beam. In Nonpatent Document 3, a phosphor of AlN thin film activated by Gd3+ was reported. However, these kinds of phosphors based on AlN are amorphous thin films which are not suitable for any application in a light or an image display device.
As a blue phosphor for applications to an image display device (VFD, FED, SED, or CRT) using an electron beam as the excitation source, a phosphor having Y2SiO5 as a host crystal and including solid-solute Ce (Patent Document 7) and a phosphor of ZnS including a solid-solute emission ion such as Ag (Patent Document 8) were reported.
The present inventor proposed a phosphor having an AlN structure crystal as a host crystal and including a divalent Eu ion (Eu2+) (i.e., AlN: Eu2+) in Patent Document 9 (not yet published). The phosphor can be obtained by firing a composite of AlN to which Si3N4 and Eu2O3 are added at the same or higher temperature than 1800° C. and exhibits blue fluorescence derived from Eu2+ as divalent Eu ions (Eu2+) are stabilized by incorporating Si, Eu, and oxygen into the AlN crystal structure as solid solutes.
Furthermore, the present inventor proposed in Patent Document 10 that a phosphor having an AlN structure crystal as a host crystal and including a divalent Eu ion was so superior in the luminance life, especially when excited with an electron beam, that an electron beam excited light-emitting device, such as the field emission display, using such a phosphor might have a long operating life.    [Patent Document 1] Specification of Japanese Patent No. 3,668,770    [Patent Document 2] Japanese Patent Application Publication No. S60-206889    [Patent Document 3] Japanese Patent Application Publication No. 2005-255895    [Patent Document 4] WO 2005/019376 pamphlet    [Patent Document 5] Japanese Patent Application Publication No. 2005-112922    [Patent Document 6] WO 2005/052087 pamphlet    [Patent Document 7] Japanese Patent Application Publication No. 2003-55657    [Patent Document 8] Japanese Patent Application Publication No. 2004-285363    [Patent Document 9] Specification of Japanese Patent Application No. 2004-234690    [Patent Document 10] Japanese Patent Application Publication No. 2006-291035    [Non patent Document 1] Meghan L. Caldwell, et al., “Visible Luminescent Activation of Amorphous AlN: Eu Thin-Film Phosphors with Oxygen”, MRS Internet Journal Nitride Semiconductor Research, Vol. 6, Num. 13, P1-8, 2001.    [Non patent Document 2] H. H. Richardson, et al., “Thin-film electroluminescent devices grown on plastic substrates using an amorphous AlN: Tb3+ phosphor,” Applied Physics Letters, Vol. 80, No. 12, p. 2207-2209, 2002.    [Non patent Document 3] U. Vetter, et al., “Intense ultraviolet cathodoluminescence at 318 nm from Gd3+-doped AlN,” Applied Physics Letters, Vol. 83, No. 11, P2145-2147, 2003.